Magnetic core



Dec. 1, 1931. A. BOYAJIAN IAGNEIIC CORE Filed May 21. 1930 CROSS REFERZRCE EXAMINE Inventor: Aram Bogqjian,

by Mm His Attonny.

we e

Patented Dec. 1, 1931 v M BOYAJIL'I', OI

rmsrmn, nssacmnsms, ABKIGNOB 1'0 em morale manna cons a umma ea m :1, 1m. mm n. 4,451.

My invention relates to magnetic cores for electrical induction apparatus such as transformers and reactors. A well designed mag- A netic core is always built up oi superposed Ii laminations of magnetic materiahthe laminations being insulated from each other to prevent excessive eddy current losses. Except in the case of very small cores, each layer or lamination is made in sections so that there are joints between the winding legand yoke sections or sometimes in other places in the core. This sectional formation of the laminations avoids excessive waste of material and, in many cases, also makes it possible to arl range them so that the magnetic flux will flow through them in the same, or approximately the same, direction in which the material was rolled. The sheets from which core laminations are cut or punched are produced W by a rolling process, and it is well known that the ma etic characteristics of a core are best when t e magnetic flux flows in the same direction as that in which its laminations were rolled.

It is usually desirable that the reluctance of the magnetic circuit of a core be as low as possible. This requires not onl that the material in the core laminations of good magnetic quality but also that any joints in the magnetic circuit have low reluctance.

At a joint in a laminated core, the lamination sections or any group of them at one side of the joint are arranged in edge to edge relation to the corresponding lamination sections or group of sections at the other side of the joint. It is not practicable to make perfect contact at a joint between the edges of the lamination sections, the ed touching at some points but being slight y separated at other points even with the care and recaution. These slight separations of the amination sections increase very appreciabl the reluctance of the magnetic circuit. e general ob'ect of the invention is to provide a laminate magnetic core with an improved form of low reluctance joint in its magnetic circuit.

The invention will be better understood from the following description taken in connection with the accompanying drawings in which Fig. 1 indicates the improved form of low reluctance joint in the magnetic circuit of a core, and Fig. 2 shows a transformer with a core having the form of core joint indicated in Fig. 1.

Like rgiiilleifiiogeucharctfirsdindicate similar parts in res o t e raw' --The invention will be explained i i cennection :with the laminated magnetic core of the transformer shown in Fig. 2. This core has winding legs 10 connected by yokes 11. The winding legs 10 are surrounded b the windin 12 from which the are insu ated by insulating cylinders 13. he yokes 11 are provided with clamps 14, each yoke and its clamps being held to ether by bolts 15. These bolts 15 engage notc es 16 in the ends of the yokes 11 to prevent relative displacement between the yokes and their clamps. Tie rods 17 extending between the clamps 14 hold the yokes tightly against the opposite ends of the winding legs 10. r

The magnetic core shown in the drawin has a simple form of butt joint in which t e edges of the laminations at each side of the joint lie in a single transverse plane and thus form a plane surface. It will be obvious, however, that other forms of joint may be used if desired. It is not practicable to'fit together two sections of a laminated core so perfectl as to avoid appreciable reluctance at the oint. The edges of the laminations may be pressed tightly together at some points but they will be slightlyseparated at other points. The reluctance of theseslight spaces in the magnetic circuit of the core is u'suall undesirable.

The reluctance o the joint or joints in the core is avoided or reduced by providing a small quantit of magnetic material 18 in each joint. This magnetic material may be a cement formed ofv fine i%ijg l i e ti c ifigm poyqder or filin mixed wi ort an cement and water or alcohol. For t e large a proportion as possible of the magnetic mixture used in the joint, only sufiicient Portland cement being used in the mixture to hold the iron powder in place in the joint after the cement has hardened. It is preferable,

st resu ts, the magnetic iron powder should form as also, that no more of the magnetic mixture beusedthanisnrytofillthesh htunavoidable spaces in the joint with t e core sections premed together into as close contact as would be posible without the mixture.

The surfaces forming the joint should be carefully finished to fit together as accurately as is practicable. A very thin layer of the magnetic mixture 18 is spread onto at least one of the joint surfaces as shown in Fig. 1. The joint is then closed with its surfaces pressed tightly to ther and referably in actual contact so r as possi 1e by means of the rods 17.

It has been found that a transformer with a core having joints made in accordance with the invention does not require as large a magiietizing current and the ma etic losses in t e core are also reduced. T e efliciency of the transformer is thus increased.

The invention has been explained by describing and illustrating it as ap lied in connection with a transformer ut various changes and applications may obviously be made without departing from the spirit of the invention or the scope of the appended claims.

What I claim as new and desire 'tosecure by Letters Ifatent of the United States, is

1. A laminated magnetic wre having a joint in its magnetic circuit, the surfaces forming said joint being pressed ti tly togethter, and a magnetic cement wit said ]0111 2. A laminated magnetic core having a joint in its magnetic circuit, the surfaces formed by the edges of the laminations at said joint being pressed tightly into contact with each other, and a magnetic cement between portions of said surfaces between their points of contact.

AiiAM BY 

